It doesn't really matter what you switch. Any of the medias inserted into your new filter will work. Media is what the filter uses to culture bacteria. (Ceramics, bioballs, sponges, floss..for example) What I have done is, take a sponge from the new filter and put it in my old filter then, take an old sponge from my present filter and put it in the new one. New tank cycled in a couple days. You can do the same with rings, noodles, bioballs, whaterver as long as you can fit it to the filter you intend to cycle. It doesn't necessarily have to come from the bottom of the filter. In my canister filter, I'll remove part of my fiberfill floss and replace with new floss. The old floss I remove is full of beneficial bacteria and great to start up new filters. I feel bad when I throw the stuff out each canister cleaning time. I've started up tanks, fully cycling in less than a week by doing the above.
